Magnetic switch sensors are widely used in consumer electronics, white goods, utility-meters (electricity meter, water meter, gas meter), automotive, and industrial applications. Presently mainstream magnetic switch sensors utilize Hall sensors and AMR (anisotropic magnetoresistive) sensors. For the Applications in consumer electronics and utility meters, Hall switch sensors and AMR switch sensors have power consumption of up to a few microamps. This is obtained at the expense of operating frequency. Hall switch sensors and AMR switch sensors are operate at a frequency of a dozen or so Hz with a switch point in the range of tens of gauss. In the automobile and other industrial fields requiring high frequency operation, Hall switch sensors and AMR switch sensors consume power on the order of mA at the kHz level.
In recent years, a new type of magnetoresistive sensor utilizing magnetic tunnel junction (MTJ) has found application in industrial fields. These combine magnetic multilayers with the tunneling magnetoresistance effect. The electrical resistance of the magnetic multilayer depends on the magnitude and the orientation of the external magnetic field. In the low-power consumption fields, such as the consumer electronics and utility-meters, the MTJ sensors operating at a frequency of a dozen Hz with a switch point of tens of gauss. In the automobile and other industrial fields requiring high frequency operation, the MTJ sensors consume power on the order of microamps at the MHz level.
Some technical descriptions of magnetic switch devices are known in the art. U.S. Patent No. 2010/0026281 A1 discloses a gradiometer comprising two sensors for measuring location and speed of magnetic targets. The use of MTJ elements in magnetic switch sensors is described by Chinese patent application #201110125153.5. These patent applications are incorporated by reference.
The power consumption for the existing switch sensors is high in both sleep working states, and they have low operating frequency. A need therefore exists for a switch sensor with high sensitivity, high frequency response, small volume, and low power consumption in sleep and working states.